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EDMONTON - Most of the world’s polar bears are likely to disappear in the next 30 to 50 years if the Arctic continues to heat up as climatologists predict, two University of Alberta scientists say.

They conducted an exhaustive review of the scientific research that has been done on the bears.

In the recent issue of the journal Global Change Biology, Ian Stirling and Andrew Derocher suggest that the bears of Hudson Bay and the Beaufort Sea in Canada and Alaska are likely to go first. And while they believe a small population of bears in northern Greenland and the Canadian Arctic islands could persist in the foreseeable future, they warn that the long-term well-being of those animals is in doubt as well.

“I have been concerned about the longer term future, not just for polar bears, but for the whole of the arctic marine system for quite a while,” says Stirling, who has been studying polar bears longer than anyone else in the world.

“When I see the trends and projections for the future for warming and sea ice loss for the long term, I think the outlook is not good for ice-breeding species ... It may be possible for a remnant population to survive for quite a while but that will also depend on what survives for them to eat.”

The latest findings are similar to those of a panel of government-commissioned scientists who warned the former U.S. Bush administration that two-thirds of the world’s polar bears could disappear by 2050 if the Arctic continues to warm at the pace that climatologists are predicting. Stirling was one of the scientists who wrote the report that led the U.S. to list the polar bear as threatened.

Since then, climate change skeptics and a handful of scientists have suggested polar bears could make the transition to life on land by eating berries, goose eggs and other things. Still others have pointed out bears made the transition to a warmer world in the past.

Stirling and Derocher could find no evidence for that optimistic scenario.

“The threat to polar bears is driven simply by habitat loss,” Derocher says. “It is no different than the situation in the Amazon. If you cut down the forest that an Amazon parrot relies on, most people grasp that the species is at risk. Unfortunately, sea ice is a much more foreign habitat for most people and its dynamic nature means that most fail to see it as a habitat.

“We can no more have polar bears with too little sea ice than we can have a forest without soil. Nobody expects a specialized parrot to suddenly adapt to a deforested habitat, yet some confer special adaptation abilities on polar bears. It’s wishful thinking for some but more often, it’s ignorance; it’s a malicious strategy intended to confuse people to create an illusion that everything’s fine.”

Polar bears, Derocher says, survived the last period of Arctic warming, but they did so at a time when there were no humans hunting them, no shipping, no oil and gas developments, and no pollution stressing them. The past period of warming was also not as intense or prolonged as this one is turning out to be.

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This grim prognosis is no longer theoretical. Declining sea ice cover in western Hudson Bay has already resulted in fewer cubs being born and surviving long enough to make it past their first year.

In Alaska, many bears are denning on land because there is insufficient ice for them to give birth offshore. Scientists there are also seeing more acts of cannibalism; bears swimming long distances and drowning bears.

“This is the third paper Ian and I have written on this theme,” says Derocher. “The first was in 1993, the second in 2004, and now 2012. The one element that has changed is that the global polar bear community has now grasped the seriousness of the issue and the number of studies indicating the dire situation for polar bears has increased dramatically. Twenty years ago, we felt that global warming was a concern for polar bears, but that it was a long ways off as a major concern. Ten years ago, the seriousness of the issue became much clearer, and 10 years from now, the situation will be clearer still.”

What concerns Derocher the most is Canada, which has two thirds of the world’s polar bears under its jurisdiction. Neither the federal nor territorial governments have altered their management for the species.

“Estimates of sustainable harvest are based on methods established 30 years ago and don’t include habitat loss as a modifying factor,” he says. “With 19 populations worldwide and 13 in Canada, we’re seeing different responses as we’d expect. Some populations are robust and healthy while others are teetering on collapse. It will take one early melt in Hudson Bay combined with one late freeze-up to push those populations into a steep decline. Our analyses suggest the bear population near Churchill could drop by half in a single year. It’s not a question of “if” but “when that will happen.”

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